Ignition system including dc-ac inverter

ABSTRACT

Electronic DC-to-AC inverter system that employs a transistor oscillator using various types of transistors. It includes means to limit reverse voltages at the base-emitter paths of the transistors. It may be included in a continuous-wave highfrequency ignition system for internal combustion engines.

Umted States Patent 1191 1111 3,808,513 Canup 1 Apr. 30, 1974 [54]IGNITION SYSTEM INCLUDING DC-AC 3,660,749 5/1972 Kadri 321/45 R XINVERTER 3,582,733 6/1971 Brubaker 321/45 R X 3,662,249 5/1972Wijsboom.... 321/45 R X 1 1 lnventorlv Robert Canup, mond. Va. 3,635,2021/1972 155161 et a1.... 123/148 E 3,164,786 1/1965 Wilson 321/45 R [73]Assgnee' Texam New York 3,119,972 1/1964 Fischman 321/45 R [22] Filed:Apr. 21, 1972 21 APP] No; 246 212 Primary ExaminerV Vil1iam M. Shoop..11. I

Attorney, Agent, or F1rmT. H. Whale C. G. R1es [52] U.S. Cl. 321/45 R,123/148 E, 331/113 A 51 Int. c1. 1102111 7/52 [57] ABSTRACT [58] held ofSearch 123/148 ggs/ Electronic DC-to-AC inverter system that employs atransistor oscillator using various types of transistors. 5 6 R f Ct dIt includes means to limit reverse voltages at the base- 1 e erences I eemitter paths of the transistors. It may be included in UNITED STATESPATENTS a continuous-wave high-frequency ignition system for 3,018,4131/1962 Neapolitakis 123/148 E X internal combustion engines. 3,536,95510/1970 Sturdevant et a1 331/113 A X 3,596,646 8/1971 Weiss 123/148 E 9Claims, 6 Drawing Figures CROSS REFERENCES TO RELATED APPLICATIONS Thisapplication relates to the copending applications Ser. No. 100,642,filed Dec. 22, 1970; Ser. No. 193,909, filed Oct. 29, 1971; and Ser. No.209,060,

filed Dec. 17,1971.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionconcerns DC-to-AC inverters in genera] and, more specifically, relatesto an improvement for an electronic circuit employing a transistoroscillator. In addition, the invention pertains to a particular use ofthe foregoing inverter in an ignition system for internal combustionengines.

2. Description of the Prior Art Heretofore, where DC-to-AC invertersemployed transistor oscillator circuits and, particularly, where suchinverters were employed in continuous-wave highfrequency ignitionsystems, there was a problem related to the maximum transistoremitter-to-base voltage which was especially severe with certain typesof transistors. For example, such characteristics are inherent intransistors using an alloy-diffused epitaxial construction. Thus, inapplications such as where an inverter is used in an ignition system forinternal combustion engines, there was difficulty with the use ofgermaniumtype and, particularly, alloy-diffused-base type transistorsbecause of the low emitter-to-base voltage rating of such transistors. Aprincipal problem related to the fact that the temperature tolerance ofgermanium-type transistors is relatively low. On the other hand, whensilicon-type transistors were employed instead of the germanium type, alimitation was found because of low reverse-voltage tolerance across thebase-emitter path of the silicon-type transistor. This was particularlytrue when epitaxial-base type of silicon transistors were considered.

Consequently, it is an object of this invention to provide an improvedoscillator circuit for use as a DC-to- AC inverter. Such inverter makesuse of low emitter-tobase breakdown voltage type transistors, with meansto. overcome the problem of failure due to a reversevoltage puncture ofthe base-to-emitter junction.

SUMMARY OF THE INVENTION Briefly, the invention concerns a DC-to-ACinverter for use in an ignition system and the like. It comprises a pairof transistors, and oscillator circuit means for connecting saidtransistors to conduct alternatively over the base-emitter path of each.It also comprises means for limiting the reverse voltage applied oversaid paths to protect against breakdown of said transistors.

Again briefly, the invention concerns a combination for use in asingle-transformer high-frequency continuous-wave ignition system forinternal combustion engines. Such combination comprises a transformerhaving a high-voltage secondary winding for delivering spark voltages tosaid internal combustion engine, and a center-tapped primary winding onsaid transformer. It also comprises a pair of transistors connected tosaid primary winding, the said transistors each having base,

collector and emitter electrodes. It also comprises at least oneoscillator feedback winding on said transformer, and circuit means forconnecting said transistors into an oscillator having base-to-emittervoltage paths. The said circuit means comprises means for limiting theamplitude of reverse-polarity voltages on said base-to-emitter voltagepaths.

' Once more, briefly, the invention concerns a combination for use in asingle-transformer high-frequency continuous-wave ignition system forinternal combustion engines. It comprises a transformer having ahighvoltage secondary winding for delivering spark voltages to saidinternal combustion engine, and a centertapped primary winding on saidtransformer, as well as a pair of transistors. The said transistors eachhave base, collector and emitter electrodes. The combination alsocomprises an oscillator feedback winding on said transformer, and firstcircuit means for connecting a DC voltage to said centertap of saidprimary winding. It also comprises second circuit means for connectingsaid collector electrodes to the ends of said primary winding, and thirdcircuit means for connecting said emitter electrodes to ground. It alsocomprises fourth circuit means including a resistor thereon forconnecting the ends of said feedback winding to said base electrodes.The third and fourth circuit means comprise portions of a completecircuit including the baseemitter paths of said transistors. Thecombination also comprises a pair of diodes, one connected between eachof said base electrodes and ground, with the polarity being such thatthe reverse voltages at said baseemitter paths are limited to theforward voltages of said diodes. The combination also comprises anignition control winding on said transformer, and anenginecontrolledmeans for cutting off and applying DC bias current in said controlwinding.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects andbenefits of the invention will be more fully set forth below inconnection with the best mode contemplated by the inventor of carryingout the invention, and in connection with which there are illustrationsprovided in the drawings, wherein:

FIG. 1 is a schematic circuit diagram illustrating a preferredmodification according to the invention.

FIG. 2 is another schematic circuit diagram illustrating a differentmodification according to the invention.

FIG. 3 is yet another schematic circuit diagram illustrating a thirdmodification of the invention.

FIG. 4 is a schematic circuit diagram of the same modification as FIG.I, but using a grounded positive and PNP transistors. 9

FIG. 5 is a schematic circuit diagram of the same modification as FIG.2, but using a grounded positive and PNP transistors.

FIG. 6 is a schematic circuit diagram of the same modification as FIG.3, but using a grounded positive and PNP transistors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 of thedrawings, it will be observed that the circuit diagram illustrates aDC-to-AC inverter, or oscillator 11. While it will be understood thatthere may be other and different uses for an inverter of this type, itis here being described as being employed in a high-frequencycontinuous-wave ignition system. Such system makes use of a transformer12 that has a high-voltage output, or secondary winding 13. Also, asindicated by an arrow 16 and the caption HIGH VOLTAGE TO DISTRIBUTOR,"the highvoltage circuit leads to the usual distributor arrangement (notshown) for an internal combustion engine.

The ignition system also includes a control winding 17 on thetransformer 12. This control winding determines the timing for theignition spark signals by controlling the oscillations of the oscillator1 1. The oscilla- -tor when oscillating develops input energy in acentertapped primary winding 18 that is located on the transformer 12.-

' The manner of controlling the starting and stopping of the oscillator11 by control winding 17 is fully described in my above-mentionedcopending applications so that no detailed reference thereto isnecessary here. It may be observed, however, that there is a source ofDC current, as indicated by the plus symbol located adjacent to acircuit connector 21. This DC source will ordinarily be a storagebattery (not shown) or the like. It would be carried by the vehicle, orotherwise situated adjacent to the internal combustion engine. Alsojoined to the circuit connector 21, there is a resistor 22 that isconnected between the DC source and the upper end (as illustrated inFIG. 1) of the control winding '17. The lower end of winding 17 isconnected via a circuit connector 25 to breaker points, or toalternative breakerless control arrangements, as indicated by thecaption.

' lator l1 employs two NPN-type transistors and 31.

These are connected so that the collector electrode of each transistor30 and 31 is connected via a circuit connector 32 and 33, respectively,to the ends of the center-tapped winding 18 on the transformer 12. Theemitter electrodes of transistors 30 and 31 are each connected to groundby a circuit connector 36 and 37, respectively. And the center tap ofwinding 18 is connected to a DC-voltage source via a connector 40 thatjoins the connector 21 mentioned earlier. Also, for the purpose of theignition system, there is a capacitor 41 that is preferably connectedwith its physical location being close to the center tap of winding 18and to engine ground.

Also, as part of the oscillator, there is a feedback winding 44 on thetransformer-l2 that has the ends thereof connected to the baseelectrodes of the transistors 30 and 31. These connections are made viacircuit connectors 46 and 47, respectively. And, there is a resistor 48connected in series in this circuit so as to limit the current flowwhich will develop as the oscillator is oscillating and, thus, limit thecurrent in the highvoltage winding 13 during the ignition event.

Previously, when this type of oscillator was-employed for an ignitionsystem it was not feasible to make use of silicon-type transistors and,particularly, epitaxial and diffused-base types, on account of the lowreversevoltage capability at the base-emitter path for such types oftransistor. However, in accordance with this invention, there is a pairof diodes 50 and 51 that are each connected in parallel across therespective baseto-emitter path of the transistors 30 and 31. This isaccomplished by having circuit connectors 54 and 55 going from one sideof each of the diodes 50 and 51 to ground. The other side of each of thediodes 50 and 51 is connected to the circuit connectors 46 and 47,respectively, which (as indicated above) lead to the base electrodes ofthe transistors 30 and 31.

It will be noted that these diodes 50 and 51 are connected with thepolarity of each such that any substantial reverse-voltage generatedcurrent flow across the base-emitter path of the transistors 30 and 31will be bypassed through the diode having a low-resistance path. Thus,as soon as the reverse voltage that is rising across the base-to-emitterpath of each transistor exceeds whatever forward-voltage rating thecorresponding diode has, it will be limited from any further increase bythe shunting effect of the low forward resistance through the diode. Inthis manner, the reverse voltage which would have been applied to eachtransistor during one-half of the oscillator cycles, will be limited toa safe value. This avoids the condition which would cause failure of thetransistors by exceeding the emitter-to-base breakdown voltage. Ofcourse, during the other half of the oscillator cycles, whenforwardvoltage conditions exist at each transistor, desirable currentflow through the base-emitter path takes place without shunting becauseof the polarity of the other diode in each case.

It may'be noted that the foregoing circuit provides a combination suchthat the transistors 30 and 31, which must pass a large current, do notneed to have a large base-to-emitter reverse-voltage breakdowncapability. Consequently, use may be made of transistors having lowemitter-to-base breakdown voltage but which have excellentcollector-to-emitter saturation voltage and switching characteristics.

The operation of the system may be described commencing with thestarting of the oscillator 1 1. Thus, the decaying magnetic flux in thecore of the transformer 12 which is caused by the engine-controlledcircuitopening of the winding 17, will induce voltages in all of thetransformer windings. When the lower end of winding 44 is positive withrespect to the upper end thereof, current will flow over the connector46 to the base of transistor 30. Then it will continue over thebaseemitter forward path of transistor 30 to ground via connector 36.From there it continues from the circuit ground via connector 55 andthrough the diode 51 to connector 47, with resistor 48 therein, and backto the upper end of the winding 44. This current flow through thetransistor 30 will turn it on, and the reverse voltage applied to theother transistor 31 across the basepositive'than the lower end. Thencurrent will flow via connector 47 and resistor 48 to the base of theother transistor 31. It continues over the forward baseemitter path oftransistor 31 to ground via connector 37. Then it goes from ground viathe connector 54 and the diode 50 back to the lower end of the winding44 via the connector 46. This limits the reverse voltage across thebase-to-emitter junction, or path of transistor to the voltage dropacross the diode which is low.

Referring to FIG. 2, there is illustrated a modified form of inverterwhich is being used in the same type of ignition system for providinghigh-frequency continuous-wave spark signals. There is a transformer 59that has a secondary, or high-voltage winding 60 to supply the sparksignals to an engine distributor (not shown) or the like. In addition,there is a center-tapped primary winding 63 and feedback winding 64, aswell as an oscillation control winding 65.

The control winding 65 acts in the same manner as was described inconnection with FIG. 1 and, similarly, there is a circuit connector 68at one end of the winding 65 which leads to engine-controlled means suchas breaker points, as indicated by the caption. Connected to the otherend of the winding 65, there are a resistor 69 and a diode 70, with theresistor 69 connected in series to a DC supply over circuit connection71.

There are a pair of NPN transistors 74 and 75 that have the oscillatorelectrodes of each connected to the ends of winding 63, while theemitter electrodes are connected to ground, as illustrated. The baseelectrodes of the transistors are connected into a series circuit withthe winding 64. This circuit may be followed from the base of transistor74 over a circuit connector 78, and via a diode 79 to a circuitconnection point 81 and a connector which leads to the one end of thewinding 64. The other end of the winding 64 is connected over aconnector 83 to a circuit connection point 84 and then via a diode 85,and on over a circuit connector 86 to the base electrode of transistor75. It will also be noted that there are two additional diodes 90 and 91that are connected with one electrode to the common circuit points 81and 84, while the opposite electrode of each is connected to ground, asillustrated.

In this case, the operation of the oscillator is substantially likethat. described above in connection with FIG. 1. It will be sufficientto note that the oscillator starts upon the opening of the circuit forenergizing winding 65 which produces a decaying magnetic flux in thetransformer 59. Such decaying flux induces a voltage in all of the otherwindings of the transformer, and when the lower end of the winding 64 ispositive with respect to the upper end, current will flow from the lowerend through diode 79, the base of transistor 74, and back through diode91, and then via a resistor 92 to complete a circuit to the upper end ofthe winding 64. Such current flow turns on the transistor 74 and startsthe oscillator into oscillation. As this action takes place, the reversevoltage across the base-emitter junction of transistor 75 will be onlythe voltage drop across the diode 91 in its forward direction which isapproximately 7/10 of a volt. When the oscillator switches and the othertransistor 75 conducts, the opposite action takes place so that thereverse voltage across the baseemitter junction of transistor 74 willhave only the voltage drop across diode 90 applied.

Referring to FIG. 3, it will" be noted that this modificationillustrates a modified oscillator circuit being used in an ignitionsystem of a similar type as those described above in relation to FIGS. 1and 2. In this case, there is a transformer 95 that has a high-voltagesecondary winding 96. In addition, there is a control winding 97 as wellas a center-tapped primary winding 98. In this modification, there is anoscillator 99, and the feedback for the oscillator is obtained from twoseparate windings 100 and 101. These windings have one end of eachconnected to ground, as illustrated. The other end of each of thesefeedback windings is connected in each case to the base electrode ofeach of a pair of transistors 104 and 105, respectively. However, inthis case, there are resistors 108 and 109 with diodes 110 and 111respectively connected in shunt thereof. Also, there is another pair ofdiodes 114 and 115 that are connected between the base electrodes andground, i.e., across the base-emitter paths of the transistors 105 and104, respectively.

The operation of the FIG. 3 system is in substance the same as the twoother modifications. It may be noted that the resistors 108 and 109 areprovided for limiting the amount of current drawn during thereverse-voltage conditions for each half of the oscillation cycle. Also,as with the other modifications, the entire ignition system includes asource of DC voltage, such as a battery 116. The control of theoscillator for creating the debreakdown voltage ratings, particularlysilicon-type transistors. Consequently, the high-temperaturecharacteristics of silicon-type transistors may be taken advantage ofwhile obviating the disadvantages of a type of transistor that has lowreverse-voltage capability.

It will be appreciated that the modifications illustrated in FIGS. 4, 5and 6 are each substantially the same in principle as the correspondingFIGS. 1, 2 and 3, respectively. The differences relate to the fact thatthe FIGS. 4, 5 and 6 modifications make use of PNP transistors insteadof NPN type. The operating principles are the same and need not bedescribed in detail. It will be noted that these modifications result ina reverse polarity, i.e. a positive ground circuit in each case.

While the invention has been described above in considerable detail inaccordance with the applicable statutes, this is not to be taken as inany way limiting the invention but merely as being descriptive thereof.

1 claim:

1. In a single-transformer high-frequency continuouswave ignition systemfor internal combustion engines, the combination comprising atransformer having a high-voltage secondary winding for delivering ACspark voltages directly to said internal combustion engine,

a center-tapped primary winding on said transformer,

a pair of transistors connected to said primary winding,

said transistors each havine base, collector and emitter electrodes,

at least one oscillator feedback winding on said transformer, circuitmeans for connecting said transistors into an oscillator havingbase-to-emitter voltage paths, said circuit means comprising a diode inshunt of said base-to-emitter voltage paths, for limiting the amplitudeof the reverse-polarity voltages, and the combination further comprisesa control winding on said transformer, and engine-controlled means forcutting off and applying a DC bias current in said control winding. 2.The invention according to claim 1, wherein the combination furthercomprises a pair of oscillator feedback windings on said transformer, aresistor in series with each of said feedback windings, and a diode inshunt of each of said resistors for permitting full current flow in theforward direction over said base-to-emitter path. 3. The inventionaccording to claim 1, wherein said transistors are diffused-base type.

4. The invention according to claim 2, wherein said transistors arediffused-base type.

5. The invention according to claim 1, wherein said transistors aresilicon type.

6. The invention according to claim 2, wherein said .a transformerhaving a high-voltage secondary winding for delivering spark voltages tosaid internal combustion engine,

a center-tapped primary winding on said transformer,

a pair of transistors,

said transistors each having base, collector and emitter electrodes,

an oscillator feedback winding on said transformer,

first circuit means for connecting a DC voltage to said center tap ofsaid primary winding,

vsecond circuit means for connecting said collector electrodes to theends of said primary winding,

third circuit means for connecting said emitter electrodes to ground,

fourth circuit means, including a resistor therein, for connecting theends of said feedback winding to said base electrodes,

a pair of diodes, one connected between each said base electrode andground with polarity for shunting reverse voltages at base-emitter pathsin excess of the forward voltages of said diodes,

an ignition-control winding on said transformer, and

transistors are silicon type.

1. In a single-transformer high-frequency continuous-wave ignitionsystem for internal combustion engines, the combination comprising atransformer having a high-voltage secondary winding for delivering ACspark voltages directly to said internal combustion engine, acenter-tapped primary winding on said transformer, a pair of transistorsconnected to said primary winding, said transistors each havine base,collector and emitter electrodes, at least one oscillator feedbackwinding on said transformer, circuit means for connecting saidtransistors into an oscillator having base-to-emitter voltage paths,said circuit means comprising a diode in shunt of said base-to-emittervoltage paths, for limiting the amplitude of the reverse-polarityvoltages, and the combination further comprises a control winding onsaid transformer, and engine-controlled means for cutting off andapplying a DC bias current in said control winding.
 2. The inventionaccording to claim 1, wherein the combination further comprises a pairof oscillator feedback windings on said transformer, a resistor inseries with each of said feedback windings, and a diode in shunt of eachof said resistors for permitting full current flow in the forwarddirection over said base-to-emitter path.
 3. The invention according toclaim 1, wherein said transistors are diffused-base type.
 4. Theinvention according to claim 2, wherein said transistors arediffused-base type.
 5. The invention according to claim 1, wherein saidtransistors are silicon type.
 6. The invention according to claim 2,wherein said transistors are silicon type.
 7. In single-transformerhigh-frequency continuous-wave ignition system for internal combustionengines, the combination comprising a transformer having a high-voltagesecondary winding for delivering spark voltages to said internalcombustion engine, a center-tapped primary winding on said transformer,a pair of transistors, said transistors each having base, collector andemitter electrodes, an oscillator feedback winding on said transformer,first circuit means for connecting a DC voltage to said center tap ofsaid primary winding, second circuit means for connecting said collectorelectrodes to the ends of said primary winding, third circuit means forconnecting said emitter electrodes to ground, fourth circuit means,including a resistor therein, for connecting the ends of said feedbackwinding to said base electrodes, a pair of diodes, one connected betweeneach said base electrode and ground with polarity for shunting reversevoltages at base-emitter paths in excess of the forward voltages of saiddiodes, an ignition-control winding on said transformer, andengine-controlled means for cutting off and applying a DC bias currentin said control winding.
 8. The invention according to claim 7, whereinsaid transistors are diffused-base type.
 9. The invention according toclaim 7, wherein said transistors are silicon type.